1. Field of the Invention
The present invention relates generally to the treatment of particulate matter by low temperature plasma and, more particularly, to the combined treatment of particulate matter by thermo-chemical energy and plasma action within a common housing.
2. Description of the Prior Art
For the purposes of the present invention, plasma may be defined as defined in U.S. Pat. No. 4,361,441 which is commonly owned with the present specification and which is hereby incorporated by reference. As in the incorporated patent, the present invention relates to low temperature plasmas (an arbitrary reference to plasmas in which the temperature of a species is below 100,000.degree. K.) and to the treatment of particulate material which includes treatment by such plasmas. In the context of the present invention, particulate material may be treated, inter alia, for the production of hot metal, the manufacture of hydraulic cements and glasses as well as for an environmentally acceptable recovery of energy from a variety of fuels and waste materials. The particulate material to be treated will depend on the particular application, including reactants desired for that application, and applications beyond those specifically discussed will be apparent to those familiar with their respective arts from the teachings contained herein.
The relatively high energy levels available from plasma have recognized value in the processing of many particulate materials. However, that energy level is relatively expensive to generate and control. Also, those energy levels are often necessary only during a portion of the processing. For example, in the reduction of iron ores (as in many other endothermic reactions) the early steps (e.g., the formation of Wustite) requires relatively small amounts of energy compared to the removal of the last oxygen to form iron. In such cases, treatment or processing entirely by plasma action, while having attributes which may not easily be attainable in other processes, is frequently viewed as wasteful in that the plasma action is not only applied at times when it is most desirable but also during other processing stages. In such cases, it is clearly desirable to employ thermo-chemical energy during the earlier, or less energy intensive, stages of the processing, while reserving the plasma energy for processing stages in which it is most useful.
While the desirability of combined thermo-chemical and plasma action for many processes would appear obvious, the implementation of their combined action has proved very troublesome. Principal among the troubles is the large volume of gases created during the thermo-chemical processing stages. These gases, which are largely combustion products, are generated by the material under process and occupy a volume which is large compared to the region or zone of plasma action. This large gas volume cannot efficiently be passed through the relatively small plasma action zone. Also, the prior art has not effectively separated the combustion gases from the material in process, especially when the later is present as submicron fumes.